Steering module over voltage issue

[imagineero]

I've bought a 2009 A3 cabrio that has been in storage for a few years and has very low mileage (a little over 10,000). The car has an issue related to the steering module. The steering module part number is 8P0 953 549 F. When the car is turned on, everything works fine. But if you start the car, after 6 seconds most of the functions related to the steering wheel stop working - indicators, hi/lo beam control, wipers, MFC for radio etc. None of these will work. If you turn the ignition off and back on again, they all work just fine. They will work indefinitely, so long as you don't start the engine. As soon as you start the engine, 6 seconds and they all stop working.

So I took it to a mechanic who tested it and told me that he is getting a fault for over voltage at the steering module and that this is causing the problem. He suggested replacing the entire steering column for thousands. I tried replacing the BCM with a known working BCM and it made no difference. The next step would probably be replacing the steering module with a known working unit. Voltage while running at idle is 14.3V which seems just fine. So I have a few questions;

• Is there any way of testing the steering module?
• Anyone have a pinout or a schematic available?
• Is the over voltage likely to be an internal fault of the steering module, or too much voltage coming in to the unit from somewhere?
• If I replace the steering module, do I also need to replace the slip ring? can they be separated?

Any advice/stories welcome.

 

[imagineero]

Bumping with a hope for assistance

 

[Sandra]

@DJAlix

 

[DJAlix]

Don't suppose you have the Error / DTC code/s that were found do you? "Over voltage" could relate to a number of different issues by the looks of things.

 

[imagineero]

Don't suppose you have the Error / DTC code/s that were found do you? "Over voltage" could relate to a number of different issues by the looks of things.

Unfortunately i don't. He was specific that it was the steering module and that the error was overvoltage at the steering module. That's all the information I have to work with. It's looking like I'll probably just order a replacement module and fingers crossed. BCM was my first guess, and I got one for not much (About AUD$160) but shipping took 5 weeks from UK even though I paid for express. We have very few spare parts for audi here in australia and prices are 5-10X world prices here. So even though the module won't be so expensive for me, it's probably some extra weeks. And if it ends up being not the issue then something else.....

Could easily end up taking 3 months for me to solve the issue which can be a bit frustrating. So any info available on testing the steering module would be of great help, especially a pinout or schematic. At least that way I've got some hope of guessing expected voltages. There's no corrosion and connections all look good. Beyond that, if the slip ring needs to be replaced together with the steering module that would be great information to have as it would save me probably a month of wait time. Any anecdotal experience is welcome - I'm clutching at straws at this stage.

 

[imagineero]

I can see if I can contact the guy over the weekend and ask if he could tell me the code, but seems unlikely as he's more interested in selling the work.

 

[imagineero]

I'm happy to report that the issue has been solved. I was unable to get the exact codes from the mechanic, but he did say that there were 2 errors - both related to the steering module. One for incorrect voltage and the other for over voltage. When the vehicle was started and everything on the steering wheel ceased to function there was a whole host of other errors related to all the things that were not working, but when the car was simply "on" and not running the only errors were related to the steering module.

While I'm loathe to simply go throwing parts at problems in the hope they will go away, there wasn't much other information to play with so I went ahead and purchased a replacement steering module locally because I found one at a good price and figured if it wasn't the issue I could most likely on sell it. The replacement module came out of an audi TT and had the matching part number 8P0 953 549 F. Be aware that there is also a HW and SW number on the module. I saw some with the same part number but with HW 034. My module had HW 036 on it. I can't comment on the difference or if they are compatible but I was able to find one with HW 036. After replacing the module my issue was solved.

Replacing the module is not that difficult but the way of replacing it is not obvious. I found that it was not necessary to remove the steering wheel/airbag to replace the module though many said it was required. It may depend on how small your steering wheel is. I found that with my wheel turned so it was upside down I was able to access the torx screw holding the module together. There are then 2 plastic clips that hold the module in place, one of them is inside the module and requires a long small screwdriver to be put in the hole in front of the module to be able to release it. There are some videos on youtube showing the process clearly. Visually there are no clues that this is how the module comes apart and you would probably break it if you didn't know the procedure.

As to the cause of the whole thing I can only speculate out of ignorance which is always a dangerous proposition. My unit and the associated wiring had nothing wrong visually. While the car is 8 years old it has only around 12,000km and has always been well cared for. I'm going to hazard a guess that the steering module contains some sort of internal regulator to step down the nominal 12V to a nominal 5V to interact with the various functions on the steering wheel, and that this regulator went out of spec. Presumably while the car was in the "on" position and producing only 12.6V, the regulator was able to step down the voltage to the required level. But with the engine running and the voltage stepping up to somewhere around 14.3, the regulator produced something higher than 5V, creating an error which caused the car to stop accepting inputs from the associated functions.

Hopefully this information is of help to someone in the future who has the same issue.